The present invention relates to a radio communication system having a random access channel for the transmission of data from a secondary station to a primary station, and further relates to primary and secondary stations for use in such a system and to a method of operating such a system. While the present specification describes a system with particular reference to the emerging Universal Mobile Telecommunication System (UMTS), it is to be understood that the techniques described are equally applicable to use in other mobile radio systems. In this specification the term random access channel refers to the logical channel on which random access transmissions take place, which would typically consist of a number of distinct physical channels.
A random access channel is a normal component of a radio communication system, enabling a Mobile Station (MS) to send short messages to a Base Station (BS). Applications include signalling to the BS when the MS is turned on, sending a packet of data to the BS when the MS may not be engaged in a call, and requesting the BS to allocate a resource for the MS to use.
In a system where mobile stations often have a requirement to send packets of data to the BS when not actually engaged in a call it is advantageous to provide a random access packet channel with similar characteristics to a standard random access channel but intended for the transmission of small and medium sized packets from a MS to the BS.
In an embodiment of a such a scheme being developed for UMTS, there are a number of random access packet channels available to a MS. A request for access to a packet channel sent by the MS is encoded with a randomly-chosen signature, which corresponds to a packet channel resource. If a suitable channel is available for use, the BS allocates it to the requesting MS.
An object of the present invention is to provide a random access channel having improved resource utilisation.
According to a first aspect of the present invention there is provided a radio communication system having a random access channel for the transmission of data from a secondary station to a primary station, the primary station having means for responding to a request from the secondary station for access to a random access channel resource, the request comprising transmission of a signal encoded with a signature corresponding to the resource, wherein the primary station has means for periodically signalling the availability of random access channel resources to secondary stations and in that the primary and secondary stations have means for dynamically re allocating signatures assigned to unavailable resources to available resources.
According to a second aspect of the present invention there is provided a primary station for use in a radio communication system having a random access channel for the transmission of data from a secondary station to the primary station, the primary station having means for responding to a request from the secondary station for access to a random access channel resource, the request comprising transmission of a signal encoded with a signature corresponding to the resource, wherein means are provided for periodically signalling the availability of random access channel resources to secondary stations and for dynamically re-allocating signatures assigned to resources that are currently unavailable to resources that are available.
According to a third aspect of the present invention there is provided a secondary station for use in a radio communication system having a random access channel for the transmission of data to a primary station, the secondary station having means for requesting access to a random access channel resource by transmitting a signal encoded with a signature corresponding to the resource, wherein means are provided for determining the availability of random access channel resources from signals periodically transmitted by the primary station and for dynamically re-allocating signatures assigned to resources that are currently unavailable to resources that are available.
According to a fourth aspect of the present invention there is provided a method of operating a radio communication system having a random access channel for the transmission of data from a secondary station to a primary station, the method comprising the secondary station requesting access to a random access channel resource by transmitting a signal encoded with a signature corresponding to the resource and the primary station responding to the request, characterised by the primary station periodically signalling the availability of random access channel resources to secondary stations and by the primary and secondary stations dynamically re-allocating signatures assigned to resources that are currently unavailable to resources that are available.